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NASA NTRSDate not supplied

Dynamical Evolution of Saturn’s Rings Driven by Micrometeoroid Bombardment

After more than a dozen years in orbit about Saturn, the Cassini mission provided key measurements that are important for determining the age of Saturn’s rings. These include the extrinsic micrometeoroid flux at Saturn, the volume fraction of non-icy pollutants in the rings, and the total ring mass. These factors help to constrain the ring age to be no more than a few 100 Myr. The Cassini Grand Finale also provided a suite of observations that demonstrate that the rings are losing mass to the planet at a surprising rate. Some of the mass flux falls as “ring rain” at higher latitudes consistent with the H3+ infrared emission pattern thought to be produced by an influx of charged water products from the rings. The contribution needed to account for the ring rain phenomenon though is considerably less than the total equatorial measured mass influx of 4800 – 45000 kg/s. Taken together, these observations imply that the rings are not only young, but also ephemeral. Here we demonstrate that bombardment by micrometeoroids, and ballistic transport of their impact ejecta can account for these observations. That is, assuming the rings began as pure ice, incoming non-icy micrometeoroids can darken the rings to their current state in the given timescale, while the dynamical effects of this bombardment process can concomitantly produce the observed mass inflow rates implying the rings were initially more massive than today. Such high continuous mass loss also suggests the rings may effectively disappear in no more than a few 100 Myr.

Paul Estrada↗
NASA NTRSDate not supplied

Simulating Micrometeoroid Bombardment on Mercury: Identifying New Space Weathering Features in the Laboratory

Airless bodies are continually exposed to the harsh interplanetary space environment, causing the alteration of their surfaces through a process known as space weathering (SW). SW is dominated by solar wind irradiation and micrometeoroid bombardment, which together alter the spectral, microstructural, and chemical characteristics of grains on the surface of airless bodies. The effects of SW are variable and depend on the heliocentric distance and the initial composition of the planetary surface, among other factors. On the Moon and S- type asteroids, it is well established that SW darkens and reddens the surface of these bodies and attenuates absorption bands across the Vis-NIR wavelengths. These spectral effects are largely the result of the production of metallic Fe nanoparticles (npFe). However, Mercury’s SW environment is unique compared to the Moon and S-type asteroids. Mercury is a geochemical endmember, with a surface composition low in Fe (<2 wt.%) and enriched in volatile components, including regions of the surface hypothesized to contain up to 4 wt.% graphite in the low reflectance material (LRM). In fact, the presence of graphite on Mercury has been hypothesized to act as a reducing agent for silicates during SW to produce Si-bearing Fe-rich metal. In addition, its location in the solar system exposes Mercury to an extreme SW environment, with the surface of the planet experiencing an intense solar wind flux and higher flux and velocity of micrometeoroid impactors compared to the Moon and S-type asteroids. The effects that such harsh SW has on materials with the unique compositional characteristics of Mercury are not well constrained. To better understand SW at Mercury, we must investigate these processes in the laboratory. Here, we present the results of our analyses of the spectral, microstructural and chemical characteristics of Mercury analog samples irradiated by pulsed laser to simulate the short duration, high temperature events associated with micrometeoroid impacts.

Nick Bott↗
NASA NTRS1971

FEP encapsulated N/P silicon solar cells after simulated micrometeoroid exposure.

The effects of simulated micrometeoroid exposure on the performance of N/P silicon solar cells encapsulated for their protection in fluorinated ethylene propylene were determined in a shock tube. It was found that the short-circuit current decreased after exposure to the simulated micrometeoroid particles. The shape of the curve remained the same and was simply translated downward with a concomitant drop in open-circuit voltage.

Mirtich, M. J.↗
NASA NTRS1977

Distribution and flux of micrometeoroids

The mass distribution, flux, and distribution in space of the micrometeoroid complex at 1 AU are estimated on the basis of data from Apollo 17 rocks and recent calibrations of solar-flare track-production rates. It is found that the size frequency distribution of microcraters on lunar rocks suggests a bimodal mass distribution of micrometeoroids, but the precise form of the curve requires further definition, particularly insofar as the degree of depletion of particles producing craters 10 to 100 microns in diameter is concerned. Variations in slope with crater-diameter or particle-mass increments are shown to indicate that different processes affect one or more particle populations. Fluxes corresponding to varied lunar surface orientation and residence time are calculated, but no striking difference is observed between the flux of submicron-diameter particles with orbits in the plane of the ecliptic and fluxes of particles with orbits normal to the plane in the solar apex direction.

Morrison, D. A.↗
NASA NTRS1986

New techniques for the detection and capture of micrometeoroids

In order to understand the origin and distribution of the biogenic elements and their compounds in the solar system, it will be necessary to study material from many classes of objects. Chemical, elemental, and isotopic measurements of returned samples of comets, asteroids, and possibly extrasolar system dust clouds would provide information on a particularly important class: the primitive objects. Extraterrestrial micron-sized particles in the vicinity of Earth are one source of such materials that might otherwise be inaccessible. The Space Station appears to be an eminently suitable platform from which to collect and detect these various particles. The primary challenge, however, is to collect intact, uncontaminated particles which will be encountered at tens of kilometers per seconds. A concept for a micrometeoroid detector that could be deployed from the Space Station was developed which uses a large area detector plate implanted with acoustic transducers. A concept of a nondestructive micrometeoroid collector for the Space Station was also developed. Particles collected would then be returned to Earth for subsequent analysis.

Wolfe, J. H.↗
NASA NTRS1992

Cracking associated with micrometeoroid impact craters in anodized aluminum alloy clamps on LDEF

The Long Duration Exposure Facility (LDEF) is a reusable hollow-cylindrical satellite sustaining a total of 57 different experiments. The 130 sq m of spacecraft surface area included anodized 6061-T6 Al alloy bay frames and clamps for holding experiment trays in the bay areas. Attention is presently given to the micrometeoroid impact crater features observed on two tray clamps recovered from the LDEF leading-edge locations. It is found that even very subtle surface modifications in structural alloy anodizing can influence micrometeoroid impact crater cracking, notable radial cracking due to the ejecta-rim of the impact craters.

Murr, Lawrence E.↗
NASA NTRS1960

Thermal Design of the Micrometeoroid Satellite S-55

The thermal design of the micrometeoroid satellite S-55 involves both experimental and analytical approaches in selecting materials and coatings. A cutaway drawing of the S-55 satellite is shown. The purpose of which is to obtain scientific and engineering design data on the frequency and penetration hazard of micrometeoroids at altitudes between about 250 nautical miles and 700 nautical miles. The passive method of thermal control used involves the selection of materials and coatings that give the desired ratio of absorptivity to emissivity alpha/epsilon for keeping the telemetry temperature within narrow limits and also to prevent overheating of the separate experiments. The selection of a material or coating for this purpose, however, is dictated not only by its absorptivity and emissivity values, but also by its reliability and the constancy of these values under long exposure to the space environment. Several test programs have been conducted in order to evaluate the materials and coatings being considered. Some of these are as follows: (1) Ultraviolet radiation in a vacuum to study discoloration and weight change. (2) Solar radiation in a vacuum to determine maximum equilibrium temperature, discoloration, and weight loss. (3) Thermal cycling and thermal shock to study material integrity (leaking, spalling, melting, etc.). (4) Proton radiation to observe effects on color, crystal structure, and strength. (5) Determination of effects of heat associated with coating application on the leak rate of pressurized parts. (6) Absorptivity and emissivity measurements. The experimental tests outlined and the maximum use of coating methods successfully employed on previous satellites should provide high reliability of the material used for the thermal design of this vehicle. A theoretical analysis was made to determine the values of alpha/epsilon required for different areas in order that the telemetry remain within the desired temperature limits.

Hastings, Earl C., Jr.↗
NASA NTRS2001

Auburn Micrometeoroid Impact Test Data Analysis

This presentation provides an overview and summary of micrometeoroid impact testing performed by Auburn University and an analysis of the test results. The testing at Auburn utilized existing facilities at Auburn to generate hypervelocity impacts into multiple layers of thin Kapton films representative of the NASA concept for the NGST sunshield. The test data consists of impactor particle mass and velocity, and for each film layer, the number and size of holes generated by the initial impact and resulting impact debris. The analysis consists of combining the test data with existing impact effects models and the micrometeoroid environment at the L2 operating location of NGST to predict sunshield degradation.

Perrygo, Charles↗
NASA NTRS2010

The Fifteen-Year Attitude History of the Wide Field Planetary Camera 2 Radiator and Collection Efficiencies for Micrometeoroids and Orbital Debris

An examination of the Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC-2) radiator assembly was conducted at NASA Goddard Space Flight Center (GSFC) during the summer of 2009. Immediately apparent was a distinct biasing of the largest 45 impact features towards one side of the radiator, in contrast to an approximately uniform distribution of smaller impacts. Such a distribution may be a consequence of the HST s attitude history and pointing requirements for the cold radiator, or of environmental effects, such as an anisotropic distribution of the responsible population in that size regime. Understanding the size-dependent spatial distribution of impact features is essential to the general analysis of these features. We have obtained from GSFC a 15 minute temporal resolution record of the state vector (Earth Centered Inertial position and velocity) and HST attitude, consisting of the orientation of the velocity and HST-sun vectors in HST body coordinates. This paper reviews the actual state vector and attitude history of the radiator in the context of the randomly tumbling plate assumption and assesses the statistical likelihood (or collection efficiency) of the radiator for the micrometeoroid and orbital debris environments. The NASA Marshall Space Flight Center s Meteoroid Environment Model is used to assess the micrometeoroid component. The NASA Orbital Debris Engineering Model (ORDEM) is used to model the orbital debris component. Modeling results are compared with observations of the impact feature spatial distribution, and the relative contribution of each environmental component are examined in detail.

Anz-Meador, Phillip D.↗
NASA NTRS2011

Micrometeoroid and Orbital Debris Threat Assessment: Mars Sample Return Earth Entry Vehicle

This report provides results of a Micrometeoroid and Orbital Debris (MMOD) risk assessment of the Mars Sample Return Earth Entry Vehicle (MSR EEV). The assessment was performed using standard risk assessment methodology illustrated in Figure 1-1. Central to the process is the Bumper risk assessment code (Figure 1-2), which calculates the critical penetration risk based on geometry, shielding configurations and flight parameters. The assessment process begins by building a finite element model (FEM) of the spacecraft, which defines the size and shape of the spacecraft as well as the locations of the various shielding configurations. This model is built using the NX I-deas software package from Siemens PLM Software. The FEM is constructed using triangular and quadrilateral elements that define the outer shell of the spacecraft. Bumper-II uses the model file to determine the geometry of the spacecraft for the analysis. The next step of the process is to identify the ballistic limit characteristics for the various shield types. These ballistic limits define the critical size particle that will penetrate a shield at a given impact angle and impact velocity. When the finite element model is built, each individual element is assigned a property identifier (PID) to act as an index for its shielding properties. Using the ballistic limit equations (BLEs) built into the Bumper-II code, the shield characteristics are defined for each and every PID in the model. The final stage of the analysis is to determine the probability of no penetration (PNP) on the spacecraft. This is done using the micrometeoroid and orbital debris environment definitions that are built into the Bumper-II code. These engineering models take into account orbit inclination, altitude, attitude and analysis date in order to predict an impacting particle flux on the spacecraft. Using the geometry and shielding characteristics previously defined for the spacecraft and combining that information with the environment model calculations, the Bumper-II code calculates a probability of no penetration for the spacecraft.

Christiansen, Eric L.↗
NASA NTRS2015

Combined Structural and Compositional Evolution of Planetary Rings Due to Micrometeoroid Impacts and Ballistic Transport

We introduce improved numerical techniques for simulating the structural and compositional evolution of planetary rings due to micrometeoroid bombardment and subsequent ballistic transport of impact ejecta. Our current, robust code is capable of modeling structural changes and pollution transport simultaneously over long times on both local and global scales. In this paper, we describe the methodology based on the original structural code of Durisen et al. (1989, Icarus 80, 136-166) and on the pollution transport code of Cuzzi and Estrada (1998, Icarus 132, 1-35). We provide demonstrative simulations to compare with, and extend upon previous work, as well as examples of how ballistic transport can maintain the observed structure in Saturn's rings using available Cassini occultation optical depth data. In particular, we explicitly verify the claim that the inner B (and presumably A) ring edge can be maintained over long periods of time due to an ejecta distribution that is heavily biased in the prograde direction through a balance between the sharpening effects of ballistic transport and the broadening effects of viscosity. We also see that a "ramp"-like feature forms over time just inside that edge. However, it does not remain linear for the duration of the runs presented here unless a less steep ejecta velocity distribution is adopted. We also model the C ring plateaus and find that their outer edges can be maintained at their observed sharpness for long periods due to ballistic transport. We hypothesize that the addition of a significant component of a retrograde-biased ejecta distribution may help explain the linearity of the ramp and is probably essential for maintaining the sharpness of C ring plateau inner edges. This component would arise for the subset of micrometeoroid impacts which are destructive rather than merely cratering. Such a distribution will be introduced in future work.

Cassini↗
NASA NTRS2017

Micrometeoroid and Orbital Debris Risk Assessment With Bumper 3

The Bumper 3 computer code is the primary tool used by NASA for micrometeoroid and orbital debris (MMOD) risk analysis. Bumper 3 (and its predecessors) have been used to analyze a variety of manned and unmanned spacecraft. The code uses NASA's latest micrometeoroid (MEM-R2) and orbital debris (ORDEM 3.0) environment definition models and is updated frequently with ballistic limit equations that describe the hypervelocity impact performance of spacecraft materials. The Bumper 3 program uses these inputs along with a finite element representation of spacecraft geometry to provide a deterministic calculation of the expected number of failures. The Bumper 3 software is configuration controlled by the NASA/JSC Hypervelocity Impact Technology (HVIT) Group. This paper will demonstrate MMOD risk assessment techniques with Bumper 3 used by NASA's HVIT Group. The Permanent Multipurpose Module (PMM) was added to the International Space Station in 2011. A Bumper 3 MMOD risk assessment of this module will show techniques used to create the input model and assign the property IDs. The methodology used to optimize the MMOD shielding for minimum mass while still meeting structural penetration requirements will also be demonstrated.

Hyde, J.↗
NASA NTRS2024

Investigating Sulfur-Rich Mercury Analogs Exposed to Simulated Micrometeoroid Bombardment in the Laboratory

Space weathering (SW) continually alters the spectral, microstructural, and chemical characteristics of the surface of airless bodies across the solar system. The effects of SW vary depending on the heliocentric distance and the initial composition of the target surface. While SW on the Moon and S-type asteroids is well documented, our understanding of how this process affects Mercury is at an early stage. Mercury’s interplanetary environment is harsh, with the surface of the planet experiencing an intense solar wind flux as well as a higher flux and velocity of micrometeoroid impactors compared to the Moon and S-type asteroids. In addition, Mercury is also a geochemical endmember, with a surface composition low in Fe (<2 wt.%) and enriched in volatile components, such as sulfur (up to 4 wt.% in the low reflectance material (LRM)). These volatile components are thought to play a major role in the formation of hollows via their sublimation. Sulfur has been hypothesized to occur at the surface of Mercury as sulfide minerals (MgS, CaS) based on its correlation with Mg and Ca in remote sensing data. However, recent observations of chaotic terrains in the north polar area of Mercury and of glacier-like features at lower latitudes indicated that octasulfur (S 8 , elemental sulfur) is another likely constituent of a volatile-rich layer in Mercury’s crust. Its behavior on Mercury may result in a complex cycle of enrichment and depletion. While S is often depleted on small body surfaces, Mercury’s gravity could result in ejected S subsequently returning to the surface and coating regolith grains. Further, the reaction of reduced S-rich gas with glasses of a Mercury-like composition also produced S-rich coatings. However, the precise behavior and evolution of S-rich species exposed to the harsh SW on Mercury remains poorly understood and needs to be further investigated in the laboratory. Here, we present the results of our analyses of the spectral, microstructural, and chemical characteristics of S-rich Mercury analogs irradiated by pulsed laser to simulate the short duration, high temperature events associated with micrometeoroid impacts.

N Bott↗